Error determination apparatus, error determination method, and storage medium

ABSTRACT

An error determination apparatus for determining a measurement error that occurs when a workpiece is measured by a coordinate measuring machine, the error determination apparatus includes an information acquisition part that acquires a) motion error information indicating a result of measuring a motion error of the coordinate measuring machine and b) design information of the workpiece, a measurement position specification part that specifies a measurement position on the workpiece on the basis of the design information, an error determination part that determines a measurement error occurring in the measurement at the measurement position due to the motion error on the basis of the motion error information, and an output part that outputs the measurement error determined by the error determination part.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent Applicationsnumber 2020-167729, filed on Oct. 2, 2020. The contents of thisapplication are incorporated herein by reference in their entirety.

BACKGROUND OF THE DISCLOSURE

Techniques for calculating a motion error generated by a coordinatemeasuring machine are known (for example, see Japanese Unexamined PatentApplication Publication No. 2015-152576).

A user of a coordinate measuring machine sometimes estimates a motionerror of the coordinate measuring machine and checks the coordinatemeasuring machine using the estimated motion error as an indicator.However, the motion error differs from a measurement error that occurswhen a workpiece is measured. Therefore, there is a problem thatdetermining the quality of the coordinate measuring machine on the basisof the motion error does not always lead to an appropriatedetermination.

BRIEF SUMMARY OF THE DISCLOSURE

The present disclosure focuses on these points, and an object of thepresent disclosure is to improve the accuracy of determining thereliability of a coordinate measuring machine.

An error determination apparatus according to the first aspect of thepresent disclosure is an error determination apparatus for determining ameasurement error that occurs when a workpiece is measured by acoordinate measuring machine, the error determination apparatus includesan information acquisition part that acquires a) motion errorinformation indicating a result of measuring a motion error of thecoordinate measuring machine and b) design information of the workpiece,a measurement position specification part that specifies a measurementposition on the workpiece on the basis of the design information, anerror determination part that determines a measurement error occurringin the measurement at the measurement position due to the motion erroron the basis of the motion error information, and an output part thatoutputs the measurement error determined by the error determinationpart.

An error determination method according to the second aspect of thepresent disclosure is an error determination method of determining ameasurement error that occurs when a workpiece is measured by acoordinate measuring machine, performed by a computer, the methodincludes the steps of acquiring a) motion error information indicating aresult of measuring a motion error of the coordinate measuring machineand b) design information of the workpiece, determining a measurementposition on the workpiece on the basis of the design information,determining a measurement error occurring in the measurement at themeasurement position due to the motion error on the basis of the motionerror information, and outputting the determined measurement error.

A non-transitory recording medium storing a program according to thethird aspect of the present disclosure stores a program for causing acomputer to determine a measurement error that occurs when a workpieceis measured by a coordinate measuring machine, the program causing thecomputer to implement functions including acquiring a) motion errorinformation indicating a result of measuring a motion error in thecoordinate measuring machine and b) design information of the workpiece,determining a measurement position on the workpiece on the basis of thedesign information, determining a measurement error occurring in themeasurement at the measurement position due to the motion error on thebasis of the motion error information, and outputting the determinedmeasurement error.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining an outline of an error determinationmethod according to the present embodiment.

FIGS. 2A and 2B are diagrams for explaining an exemplary measurementerror C1 determined by an error determination apparatus 10.

FIG. 3 is a diagram for explaining a configuration of the errordetermination apparatus 10.

FIG. 4 is a flowchart for explaining an operation of the errordetermination apparatus 10.

DETAILED DESCRIPTION OF THE DISCLOSURE

Hereinafter, the present invention will be described through exemplaryembodiments of the present invention, but the following exemplaryembodiments do not limit the invention according to the claims, and notall of the combinations of features described in the exemplaryembodiments are necessarily essential to the solution means of theinvention.

<An Outline of an Error Determination Method According to the PresentEmbodiment>

FIG. 1 is a diagram for explaining an outline of an error determinationmethod according to the present embodiment. Referring to FIG. 1 , anoutline of a) a method for determining a measurement error that occurswhen a workpiece is measured by a coordinate measuring machine using anerror determination apparatus 10 and b) a method for determining thepresence or absence of an abnormality in the coordinate measuringmachine on the basis of the determined measurement error is described.

A CMM model A1 is a model that outputs a measurement error of acoordinate measuring machine when various conditions for measuring aworkpiece with the coordinate measuring machine are inputted. When acomputer executes a program, it functions as the CMM model A1 thatoutputs the measurement error on the basis of the inputted information.On the basis of motion error information B1, design information B2, andmeasurement condition information B3 inputted, the CMM model A1 outputsthe measurement error that occurs when the coordinate measuring machineperforms measurement corresponding to these pieces of information.

The motion error information B1 is information indicating a result ofmeasuring the motion error of the coordinate measuring machine (that is,a coordinate measuring machine as a target whose measurement error is tobe determined) corresponding to the CMM model A1. The motion errorincludes a) a translational error such as a scale error or a squarenesserror and b) a rotational error, for example. The motion errorinformation B1 includes a value of the motion error determined on thebasis of a result of a daily inspection of the coordinate measuringmachine, for example.

The design information B2 is design information of the workpiece. Thedesign information is information for specifying geometry, length,thickness, and the like of the workpiece, and is Computer Aided Design(CAD) data of the workpiece, for example.

The measurement condition information B3 is information indicating ameasurement condition when the coordinate measuring machinecorresponding to the CMM model A1 measures the workpiece. Themeasurement condition includes, for example, a construction of thecoordinate measuring machine, properties of a probe provided to thecoordinate measuring machine, a location of the workpiece, anorientation of the workpiece during measurement, and a measurement pointon the workpiece.

A measurement error C1 is a measurement error that occurs due to themotion error and the measurement condition when the coordinate measuringmachine corresponding to the CMM model A1 measures the workpiece. Themeasurement error C1 is a measurement error that occurs when theworkpiece is measured under a condition indicated by the measurementcondition information B3.

In the error determination method shown in FIG. 1 , after themeasurement error C1 is determined, a decision processing part A2compares the measurement error C1 to a tolerance indicated by toleranceinformation B4 of the workpiece, to decide whether the coordinatemeasuring machine is normal. For example, if the measurement error C1 islarger than the tolerance, the error determination apparatus 10 outputsa decision result C2 that there is an abnormality in the coordinatemeasuring machine. By using such an error determination apparatus 10 toimprove the accuracy of determining the reliability of the coordinatemeasuring machine, it is possible to ascertain before measurementwhether a reliable measurement result can be obtained when thecoordinate measuring machine measures the geometry of the workpiece thatneeds to be measured.

FIGS. 2A and 2B are diagrams for explaining an exemplary measurementerror C1 determined by the error determination apparatus 10. FIG. 2Ashows measurement of the workpiece with no motion error occurring. FIG.2B shows measurement of the workpiece when a motion error occurs due toyawing in a Y-direction. It should be noted that, for simplicity ofexplanation, FIGS. 2A and 2B show examples of measuring a squareworkpiece W using a coordinate measuring machine including an X-stageXS, a Y-stage YS, and a probe P.

As shown in FIG. 2A, in measuring the workpiece W with no motion error,there is no need to consider the motion error when estimating themeasurement error in measuring the workpiece W with the coordinatemeasuring machine. However, as shown in FIG. 2B, if an XY squarenesschanges due to yawing in the Y-direction, for example, the measurementof the workpiece W will contain the motion error that can be specifiedon the basis of a product of a length L and a rotation error θ. The CMMmodel A1 is used for determining the measurement error C1 as a productof the length L and the rotation error θ. The product corresponds to themotion error at a position where the probe P and the workpiece W contacteach other.

<A Configuration of the Error Determination Apparatus 10>

FIG. 3 is a diagram for explaining a configuration of the errordetermination apparatus 10. The error determination apparatus 10includes a storage 11 and a controller 12. The storage 11 includes astorage medium such as a Read Only Memory (ROM), a Random Access Memory(RAM), a hard disk, and the like. The storage 11 stores a program to beexecuted by the controller 12.

The controller 12 is a CPU (Central Processing Unit), for example. Thecontroller 12 functions as an information acquisition part 121, ameasurement position specification part 122, an error determination part123, a decision part 124, and an output part 125, by executing theprogram stored in the storage 11. The controller 12 functions as the CMMmodel A1 shown in FIG. 1 , with the information acquisition part 121,the measurement position specification part 122, and the errordetermination part 123 working together. The decision part 124 and theoutput part 125 function as the decision processing part A2 shown inFIG. 1 .

The information acquisition part 121 acquires information required fordetermining the measurement error C1 and outputting the decision resultC2. The information acquisition part 121 acquires the informationthrough a communication network such as a LAN (Local Area Network).

The information acquisition part 121 acquires the motion errorinformation B1, which indicates the result of measuring the motion errorof the coordinate measuring machine, from a computer (not shown infigures) that stores the result of the daily inspection of thecoordinate measuring machine, for example. The information acquisitionpart 121 acquires the design information B2 of the workpiece from acomputer (not shown in figures) that stores CAD data of the workpiece,for example. The information acquisition part 121 outputs the motionerror information B1 to the error determination part 123, and outputsthe design information B2 to the measurement position specification part122.

The information acquisition part 121 further acquires, for example, themeasurement condition information B3, indicating a plurality ofmeasurement conditions when the coordinate measuring machine measuresthe workpiece, from a computer (not shown in figures) of a person whomeasures the workpiece. The measurement condition information B3includes a) characteristic information indicating characteristics of theprobe that contacts the workpiece and b) position information indicatinga location of the workpiece in the coordinate measuring machine. Thecharacteristics of the probe include a size, length, orientation, andconfiguration of a stylus provided to the probe, for example. Theinformation acquisition part 121 outputs the measurement conditioninformation B3 to the error determination part 123.

The information acquisition part 121 further acquires the toleranceinformation B4 indicating the tolerance of the workpiece from thecomputer storing the CAD data of the workpiece, for example. Thetolerance indicated by the tolerance information B4 includes geometrictolerances for straightness, flatness, parallelism, squareness, and thelike of the workpiece, for example. The information acquisition part 121outputs the tolerance information B4 to the decision part 124.

It should be noted that the computer storing the result of the dailyinspection of the coordinate measuring machine, the computer storing theCAD data of the workpiece, and the computer of the person who measuresthe workpiece may be the same computer, or may be different computers.

The measurement position specification part 122 specifies themeasurement position on the workpiece on the basis of the designinformation B2 acquired by the information acquisition part 121. Themeasurement position is a position of a feature point of the workpiece,such as a vertex, for example. The measurement position on the workpieceis represented by the direction and distance to the reference positionof the workpiece, for example. The measurement position specificationpart 122 may specify the measurement position on the basis of themeasurement point indicated by the measurement condition information B3with the design information B2. The measurement position specificationpart 122 notifies the error determination part 123 about the specifiedmeasurement position on the workpiece.

On the basis of the motion error information B1, the error determinationpart 123 determines the measurement error C1 that occurs in ameasurement at the measurement position due to the motion error. Forexample, on the basis of the motion error information B1 obtained by theinformation acquisition part 121, the error determination part 123determines the measurement error C1, such as a translation error or arotation error that occurs at each of the plurality of measurementpositions specified by the measurement position specification part 122.

Motion errors that occur in the coordinate measuring machine aredifferent depending on the measurement position because the distance anddirection in which the probe moves changes depending on the measurementposition, for example. The error determination part 123 specifies thedistance and direction in which the probe moves on the basis of themeasurement position, and determines the motion error corresponding tothe specified direction and distance, thereby determining themeasurement error C1 with high calculation accuracy.

The error determination part 123 determines the measurement error C1further on the basis of one or more measurement conditions that affectthe measurement at the measurement position among the plurality ofmeasurement conditions indicated by the measurement conditioninformation B3. For example, when the measurement condition informationB3 includes the characteristic information indicating thecharacteristics of the probe that contacts the workpiece, the errordetermination part 123 determines the measurement error C1 that occurswhen the probe contacts the measurement position on the basis of thecharacteristics of the probe.

Motion errors that occur in the coordinate measuring machine aredifferent depending on the position of the stylus in contact with theworkpiece, for example. By specifying the position of the stylus incontact with the workpiece at the measurement position on the basis ofthe characteristic information of the probe, the error determinationpart 123 determines the measurement error C1 at the measurement positionby taking into account the position of the stylus where the styluscontacts the workpiece.

When the measurement condition information B3 includes the positioninformation indicating the location of the workpiece in the coordinatemeasuring machine, the error determination part 123 may determine themeasurement error on the basis of the motion error corresponding to thelocation indicated by the position information. The location isrepresented by coordinates in the Cartesian coordinate system of a spacethat can be measured by the coordinate measuring machine. The errordetermination part 123 specifies the measurement position in theCartesian coordinate system of the space that can be measured by thecoordinate measuring machine, on the basis of the measurement positionspecified by the measurement position specification part 122 and thelocation indicated by the position information.

Subsequently, the error determination part 123 specifies the distanceand direction in which the probe moves on the basis of the specifiedmeasurement position. The error determination part 123 determines themeasurement error C1 at each of the plurality of measurement positionson the basis of the length and the like of the probe at each of theplurality of measurement positions specified on the basis of thedistance and direction in which the probe moves. The error determinationpart 123 can determine the measurement error C1 at the measurementposition by measuring the measurement error on the basis of the motionerror corresponding to the location of the workpiece in this way.

The decision part 124 compares the measurement error C1 determined bythe error determination part 123 to the tolerance of the workpieceindicated by the tolerance information B4 acquired by the informationacquisition part 121, and decides whether the measurement error C1 iswithin an acceptable range on the basis of a result of the comparing.The decision part 124 compares each of the plurality of motion errorsincluded in the measurement error C1 with the tolerances of theworkpiece respectively corresponding to the motion errors.

Specifically, the decision part 124 decides that the measurement errorC1 is not within the acceptable range if one or more of the plurality ofmotion errors included in the measurement error C1 exceeds thetolerances of the workpiece respectively corresponding to the one ormore motion errors. On the other hand, if each of the plurality ofmotion errors included in the measurement error C1 is less than or equalto the tolerances of the workpiece respectively corresponding to theplurality of motion errors, the decision part 124 decides that themeasurement error C1 is within the acceptable range. The decision part124 notifies the output part 125 of the decision result.

The output part 125 outputs the measurement error C1 determined by theerror determination part 123. In this case, the output part 125 outputsthe measurement error C1 associated with each of the plurality ofmeasurement positions on the workpiece. The output part 125 outputs theresult of comparing the tolerance indicated by the tolerance informationB4 and the measurement error C1. The result of comparing is a result ofthe decision of the decision part 124 concerning whether or not themeasurement error C1 is within the acceptable range, and corresponds tothe decision result C2.

The output part 125 outputs the measurement error C1 and the decisionresult C2 to an information device such as a computer or a smart phone,or to the coordinate measuring machine, via a communication network. Forexample, when the error determination apparatus 10 is formed by aninformation device such as a computer or a smart phone, the output part125 displays the measurement error C1 and the decision result C2 on adisplay included in the information device.

By outputting or displaying the measurement error C1 and the decisionresult C2 in this way, the user of the coordinate measuring machine canknow the measurement error that occurs when a workpiece is measuredusing the coordinate measuring machine and determine the reliability ofthe coordinate measuring machine, for example. Specifically, the user ofthe coordinate measuring machine can decide whether or not to repair thecoordinate measuring machine on the basis of the result of determiningthe measurement error that occurs when the workpiece is measured.

<A Flowchart of the Error Determination Apparatus 10>

FIG. 4 is a flowchart for explaining an operation of the errordetermination apparatus 10. The information acquisition part 121acquires the motion error information B1 (step S11). The informationacquisition part 121 acquires the design information B2 (step S12). Theinformation acquisition part 121 acquires the measurement conditioninformation B3 (step S13). The measurement position specification part122 specifies the measurement position on the basis of the designinformation B2 (step S14). The error determination part 123 determinesthe measurement error C1 on the basis of the measurement positionspecified by the measurement position specification part 122 (step S15).

The information acquisition part 121 acquires the tolerance informationB4 (step S16). When the error determination part 123 determines themeasurement error C1, the decision part 124 compares the toleranceindicated by the tolerance information B4 to the measurement error C1.If each of the plurality of motion errors indicated by the measurementerror C1 is equal to or less than the tolerance respectivelycorresponding to the motion errors (YES in S17), the decision part 124decides that the measurement error C1 is in the acceptable range, andoutputs “OK” as the decision result (step S18). If one or more motionerrors of the plurality of motion errors indicated by the measurementerror C1 exceed the tolerances corresponding to the motion errors (NO inS17), the decision part 124 decides that the measurement error C1 is notin the acceptable range, and outputs “NG” as the decision result (stepS19).

<Effects of the Error Determination Apparatus 10>

As described above, the error determination apparatus 10 includes themeasurement position specification part 122 that specifies themeasurement position of the workpiece on the basis of the designinformation. Then, the error determination part 123 determines themeasurement error that occurs in the measurement at the measurementposition specified by the measurement position specification part 122 onthe basis of the motion error information. The error determinationapparatus 10 operates in this manner, and so the error determinationapparatus 10 can determine the measurement error in the coordinatemeasuring machine while taking into account the motion error thatchanges depending on the measurement position on the workpiece. Then,the user of the coordinate measuring machine can determine thereliability of the coordinate measuring machine on the basis of themeasurement error determined by the error determination apparatus 10. Asa result, the user who measures the workpiece using the coordinatemeasuring machine can a) confirm whether or not the coordinate measuringmachine can appropriately measure the workpiece prior to the measurementand b) appropriately determine whether or not the coordinate measuringmachine needs to be repaired.

The present disclosure is explained on the basis of the exemplaryembodiments. The technical scope of the present disclosure is notlimited to the scope explained in the above embodiments and it ispossible to make various changes and modifications within the scope ofthe disclosure. For example, all or part of the apparatus can beconfigured to be functionally or physically distributed and integratedin arbitrary units. Further, new exemplary embodiments generated byarbitrary combinations of them are included in the exemplary embodimentsof the present disclosure. The effect of the new embodiment caused bythe combination has the effect of the original embodiment together.

What is claimed is:
 1. An error determination apparatus for determininga measurement error that occurs when a workpiece is measured by acoordinate measuring machine, the error determination apparatuscomprising: a controller configured to: acquire a) motion errorinformation indicating a result of measuring a motion error due to atleast one of a scale error, a translational error, or a rotational errorat a time of measuring in advance in a plurality of positions in a spacethan can be measured by the coordinate measuring machine, b) designinformation of the workpiece, and c) position information indicating alocation of the workpiece in the coordinate measuring machine; specify ameasurement position on the workpiece on the basis of the designinformation; determine a measurement error occurring in the measurementat a contact position of a stylus included in a probe in a Cartesiancoordinate system of the space that can be measured by the coordinatemeasuring machine and specified on the basis of the location of theworkpiece and the measurement position on the workpiece on the basis ofthe design information due to the motion error occurring in the contactposition by referencing the motion error information; and output thedetermined measurement error.
 2. The error determination apparatusaccording to claim 1, wherein the controller is further configured to:acquire measurement condition information indicating a plurality ofmeasurement conditions when the workpiece is measured by the coordinatemeasuring machine, and determine the measurement error further on thebasis of one or more measurement conditions that affect the measurementat the measurement position among a plurality of measurement conditionsindicated by the measurement condition information.
 3. The errordetermination apparatus according to claim 2, wherein the motion erroris a rotational error; the measurement condition information includescharacteristic information indicating a length of the stylus thatcontacts the workpiece, and the controller is further configured to:determine the measurement error that occurs when the stylus contacts themeasurement position by multiplying the length of the stylus by therotational error at the contact position.
 4. The error determinationapparatus according to claim 1, wherein the controller is furtherconfigured to output the determined measurement error in associationwith each of a plurality of positions on the workpiece.
 5. The errordetermination apparatus according to claim 1, wherein the controller isfurther configured to: acquire tolerance information indicating atolerance of the workpiece, and output a result of comparing thetolerance indicated by the tolerance information and the measurementerror.
 6. The error determination apparatus according to claim 5 whereinthe controller is further configured to: determine that the measurementerror is not in an acceptable range if the measurement error exceeds thetolerance of the workpiece, and determine that the measurement error isin the acceptable range if the measurement error is equal to or lessthan the tolerance of the workpiece, and output a result of thedetermination.
 7. An error determination method of determining ameasurement error that occurs when a workpiece is measured by acoordinate measuring machine, performed by a computer, the methodcomprising: acquiring a) motion error information indicating a result ofmeasuring a motion error due to at least one of a scale error, atranslational error, or a rotational error at a time of measuring inadvance in a plurality of positions in a space that can be measured bythe coordinate measuring machine, b) design information of theworkpiece, and c) position information indicating a location of theworkpiece in the coordinate measuring machine; determining a measurementposition on the workpiece on the basis of the design information;determining a measurement error occurring in the measurement at acontact position of a stylus included in a probe in a Cartesiancoordinate system of the space that can be measured by the coordinatemeasuring machine and specified on the basis of the location of theworkpiece and the measurement position due to the motion error occurringin the contact position by referencing the motion error information; andoutputting the determined measurement error.
 8. A non-transitoryrecording medium storing a program for causing a computer to determine ameasurement error that occurs when a workpiece is measured by acoordinate measuring machine, the program causing the computer toimplement functions comprising: acquiring a) motion error informationindicating a result of measuring a motion error due to at least one of ascale error, a translational error, or a rotational error at a time ofmeasuring in advance in a plurality of positions in a space that can bemeasured by the coordinate measuring machine, b) design information ofthe workpiece, and c) position information indicating a location of theworkpiece in the coordinate measuring machine; determining a measurementposition on the workpiece on the basis of the design information;determining a measurement error occurring in the measurement at acontact position of a stylus included in a probe in a Cartesiancoordinate system of the space that can be measured by the coordinatemeasuring machine and specified on the basis of the location of theworkpiece and the measurement position, due to the motion erroroccurring in the contact position by referencing the motion errorinformation; and outputting the determined measurement error.